Vitamin A and its active metabolite, retinoic acid (RA), affect the immune system in multiple ways. Our research is focused on the ability of retinoids to work together with co-stimulatory molecules, of both endogenous and exogenous origin, to promote strong and long-lasting immunity in adults and neonates. Using mice, we have recently shown that a nutritional-immunological combination of RA and a cytokine inducer, poly-l:C (PIC), can act together to stimulate much stronger primary and memory antibody responses in both adult and neonatal mice. Our long-term goal is to understand how RA and co-stimuli can augment antigen-specific antibody responses, especially in the very young and in individuals whose immune system is weakened by vitamin A deficiency or disease. The central hypothesis of this proposal is "Retinoic acid, an active metabolite of VA, cooperates with immunological co-stimuli - especially the Toll-like Receptor (TLR)-3 ligand, poly-l:C (PIC), the signaling co-receptor CD38, and tumor necrosis factor family members - to significantly regulate antibody production at both the neonatal and adult stages of life." We will use a combination of cell and molecular analysis, flow cytometry, confocal microscopy, and immunoassays to better understand how RA and co-stimuli promote the activation of B-cells and the antibody response to immunization in vivo. Our 3 aims are: 1) To determine how RA and costimulatory molecules activate B cells isolated from adult and neonatal mice;2) To establish how RA and co-stimulation regulate the formation of germinal centers (GC), a specialized microenvironment where antibody-producing cells mature;3) To test whether a special population of T-cells, referred to as iNKT cells, are responsive to RA plus costimuli, and whether a combined nutritional-immunological treatment can balance the production of cytokines that are needed for an optimal immune response. Relevance: Vaccination is a life-saving strategy for infants and children. Vitamin A's active metabolite, retinoic acid, together with immune stimuli of endogenous and exogenous origin, may be an effective combination for promoting B-lymphocyte activation and the production of a strong, durable antibody response in vivo, as is necessary for protection against infectious disease. Our studies will use biochemical and microscopic techniques to test whether nutritional-immunological combinations of RA plus several immune stimuli, given with immunization, can promote B-cell activation, induce microarchitectural changes needed for strong antibody production, and increase the plasma antibody levels in adult and neonatal mice.